FIG. 1 shows a cross-section of a gas turbine engine that has a compressor and turbine in back-to-back relation. Disposed between these two components is a prior art, one piece pilot ring 54. The pilot ring 54 serves two functions referred to as a radial function and an axial function.
The radial function is maintaining concentricity between the compressor rotor 35 and the turbine rotor 37. This requires the pilot ring 54 to maintain radial contact with both rotors during assembly of the engine and during operation. During operation of the engine, the radial growth due to thermal expansion of the turbine rotor is significantly greater than that of the compressor rotor. As a result, the pilot ring 54 must roll to accomplish the radial function.
The axial function is transferring the axial load between the two rotors which requires that the axial ends of the ring remain parallel. As a consequence, the ring cannot roll freely as the turbine rotor thermally grows at a faster rate than the compressor rotor, requiring large radial interference fits between the pilot ring and the rotors. Some of the disadvantages associated with large interference fits are that they require a large temperature difference of the components during assembly, the ring can pop off the compressor rotor if assembly is not completed quickly, clocking of the turbine relative to the compressor to achieve balance and "run out" is difficult, and large stresses can be generated in the ring causing it to yield which in turn can result in high vibrations in the engine.
Accordingly, there is a need for a pilot ring that overcomes the disadvantages of prior art pilot rings.